In manufacturing semiconductor elements, lithographic technology has been employed in which a photoresist coating is formed on a substrate such as a silicon wafer and, after selectively irradiating the coating with actinic rays, development treatment is conducted to form a resist pattern on the substrate thereby.
In recent years, in order to attain higher degree of integration in LSI, patterning technology for forming patterns with a finer line width in a lithographic process has been making a rapid progress. For forming a pattern with a finer line width, various proposals have been made with respect to all steps of the lithography and all materials to be used therein including photoresists, antireflective coatings, exposing methods, exposing apparatus, developing agents, developing processes and developing apparatus. For example, Japanese Patent Publication No. 2,643,056 and Japanese Unexamined Patent Publication No. H7-181685 describe that an antireflective surface coating containing a fluorine-containing compound with a low refractive index is formed on a resist coating to prevent detrimental influences of reflected light from the resist surface on formation of a resist pattern thereby. When an antireflective coating is coated on a resist layer, degree of vibration amplitude of the thickness of a resist coating v.s. sensitivity curve becomes smaller. Therefore fluctuation in sensitivity of resist becomes smaller even when thickness of the resist layer fluctuates, which leads the advantage of a decreased fluctuation in dimension of resist patterns formed. In addition, the antireflective surface coating serves to decrease standing wave to be caused by interference between incident light and reflected light or between one reflected light and another reflected light. Recently, technology of forming a resist pattern having a desired line width without providing the antireflective surface coating has also been developed. As examples thereof, there are illustrated that an underlying substrate is made plane to depress fluctuation in dimension due to fluctuation in thickness of the resist layer as described above, or a mask pattern is finely adjusted in advance according to fluctuation in dimension of the resist.
With regard to exposing apparatus, there has been proposed a process of using a light source emitting radiation of a short wavelength, which is advantageous for formation of a superfiner pattern, such as deep UV rays of KrF excimer laser (248 nm) or ArF excimer laser (193 nm) or, further, X rays or electron beams, and some of them have been coming into practice.
On the other hand, improvement in the yield of semiconductor integrated circuits has been paid attention as an extremely important matter in manufacturing them. There exist many factors by which the yield of semiconductor integrated circuits is decided. One of the factors is patterning failure upon forming a pattern using a resist. This patterning failure of a resist pattern is caused, for example, by the dust existing in the resist or sticking onto the surface of the resist layer, by the deterioration of the resist due to floating chemical species in the clean room, by the coating failure of the resist or the like, or by the development failure. As an example of deterioration due to chemical species floating in a clean room, there is given a process using a chemically amplified photoresist. In this process, the chemically amplified photoresist is susceptible to influence of acidic substances, basic substances and moisture in the atmosphere. Therefore, when the period between pattern-wise exposure and PEB (post exposure bake) is prolonged (post exposure delay) or due to intermixing with a resist, there results a change in dimension of a pattern, for example, by formation of a T-topped resist pattern in the case where a positive-working photoresist is used as resist, or formation of a round-topped resist pattern in the case where a negative-working photoresist is used as resist.
In addition, defects upon developing a resist layer have become a problem. As examples of defects upon development, there are given formation of scum in line-and-space type resists and hole-opening failure in contact hole type resists. Several causes may be considered for the hole-opening failure of contact holes, but the most popular hole-opening failure is one caused by residues after development. As a cause of these defects, there is illustrated insufficient dissolution of exposed portions into a developing solution due to insufficient contact between the developing solution containing water as a major component and the surface of a resist coating upon bringing the developing solution into contact with the resist surface, which leads to hole-opening failure of portions which are designed to open essentially. It is also thought that hardly-solubles in the developing solution might re-deposit onto the surface of the resist upon rinsing with water after development.
Further, it is necessary to enhance contrast of a resist in order to form a finer pattern. In general, in order to improve contrast of a contact hole type resist, a technique of increasing a protecting ratio of hydrophilic groups in a major component polymer is used with respect to, for example, positive-working chemically amplified photoresists. However, when the protecting ratio is increased, the resist surface is liable to become hydrophobic, leading to deterioration in wetting properties for the developing solution.
Various investigations have been conducted to solve the above-described problems. For example, Japanese Unexamined Patent Publication No. H9-246166 proposes to treat the surface of a photoresist with plasma to render the surface hydrophilic thereby, thus improving wetting properties of the resist for a developing solution and decreasing development defects. This technique, however, requires introduction of an additional apparatus for the plasma treatment as well as includes the problem of decrease in throughput.
In addition, various attempts for decreasing the development defects by optimizing development sequence have been made as well. For example, Japanese Examined Patent Publication No. H4-51020 describes to improve wetting properties of a positive-working resist for a developing solution by adding an acetylenealcohol type surfactant to the developing solution, thereby forming a pattern having no development defects. Although some effects can be obtained by this technique, the effects are at present still insufficient in ultra-fine working using the aforesaid chemically amplified photoresists. In addition, Japanese Unexamined Patent Publication No. S61-179435 describes a method of optional formation of surface coating, which is effective for improving wetting properties for a developing solution, as well as a method of adding a surfactant to the developing solution and a method of plasma-treating the surface of a resist coating, for preventing development defects resulting from lack of wetting properties for the developing solution.
Particularly in the case where surface coating for decreasing the development defects is formed on a chemically amplified photoresist, there may cause a round-topped or a T-topped pattern which may cause a trouble in an etching process when a surface coating composition, which is coated to reduce this development-defect, is compatible with a chemically amplified resist. For example, in the patent publication of JP 2643056, as an anti-reflective coating composition to form an anti-reflective coating on a photoresist film, a composition comprising a water-soluble polymer binder and a water-soluble fluorocarbon compound (for example, a quaternary ammonium salt of perfluorocarboxylic acid or perfluorosulfonic acid, and so on) was disclosed. However, in said publication, there is no description of a control on the amount of reduced thickness in film thickness after developing a chemically amplified photoresist. In addition, the method described in the publication has a problem. That is, in the case where the anti-reflective coating composition described in said publication is used, when the chemically amplified photoresist is a positive-working photoresist, a pattern profile of a resist pattern formed is likely to become a T-letter-shape (T-top), and when being a negative-working photoresist, the pattern profile of the resist pattern formed is likely to become a round shape (round-top), thereby a problem of pattern dimension deterioration being taken place.
Further, it is said that problems in attaining uniform thickness of coating and uniform development to be caused with a recent increase in diameter of a substrate such as a silicon wafer make it difficult to form a finer pattern. For example, a paddle developing method has so far been popularly employed for developing a resist coating on the silicon wafer. In the paddle developing method, a developing solution is dropped onto a resist coating formed on a substrate, and the substrate is spun to form a thin film of the developing solution all over the resist coating, thus development of the resist coating being conducted. However, there generates a difference in circumferential speed between the central portion and the peripheral portion of the substrate, thereby a difference in speed of the coating generating. Thus, developing conditions become different between the central portion of the wafer and the peripheral portion thereof. In this situation, particularly when a chemically amplified photoresist is used as a resist and a developing process of a large-diameter substrate having a diameter of 8 inches or more is conducted, development defects in the peripheral portion are caused in some cases which have not conventionally been observed in treating a resist coating formed on a substrate having a diameter of 6 inches or less.
Therefore, in order to improve a yield in manufacturing semiconductor integrated circuits and so on, a process for forming a resist pattern has been desired which enables one to reduce development defects to be caused upon development including a development defect of a chemically amplified photoresist in the periphery of a larger diameter substrate such as a silicon wafer caused by increasing in diameter of a substrate, and which does not cause pattern failure such as T-top or round top after development for coping with formation of finer patterns earnestly for forming a finer resist pattern.
As a method to reduce such development defects, Japanese Unexamined Patent Publication No. 2002-6514 describes that by applying a composition for reducing a development-defect containing a fluorine-containing surfactant on a chemically amplified photoresist coating, the amount of reduced thickness in film thickness of the chemically amplified photoresist after exposure to light and development is made bigger by further 10 Å to 500 Å compared with the case without applying this composition for reducing development-defects to form a pattern without development-defect thereby. In this publication, as a surfactant which is contained in a composition for reducing development-defects of a positive-working chemical amplified photoresist, it is disclosed to use a surfactant which is formed with excess of acid for the composition ratio of organic acid and base and in which at least acid remains. However, it is difficult to make this film thickness reduction large by using the composition for reducing development-defects. When elimination of T-top can be realized in the case where film thickness reduction would be made large, there is a limit to form a pattern with good profiles by using the composition for reducing development-defects. In addition, in the publication, there is no description that a film thickness reduction can be controlled quantitatively. Because of this there is a problem that it is difficult to obtain the composition for reducing development-defects which can provide an optimal film thickness reduction in order to make the pattern-profiler rectangular and good.
In consideration of the above-described situation, an object of the present invention is to provide a process of forming a resist pattern by using a composition for preventing development defects by which development defects of a positive-working chemically amplified photoresist is particularly reduced upon developing of a large diameter substrate having a diameter of 8 inches or more and deterioration of pattern profiles does not be caused such as T-top or round top which are inconvenient for an etching step due to detrimental influences of a processing atmosphere and intermixing between the surface coating and the resist, wherein an occurrence of development defects on a substrate with large diameter and a pattern profile after development can be improved with optimal film thickness reduction by use of a composition for preventing development defects which can make a film thickness reduction after development bigger compared with the process so far known as well as control the amount of film thickness reduction, and coping with optimal film thickness reduction is easy.
Another object of the present invention is to provide a composition for preventing development-defects used in above-described process.
As a result of intensive investigations, the inventors have found that in a process of forming a resist pattern in which a composition for preventing development-defects containing a particular fluorine-containing surfactant is applied on a positive-working chemically amplified photoresist to render the surface thereof hydrophilic, then pattern-wise exposed to light and developed, the amount of film thickness reduction subsequent to a development of a positive-working chemically amplified photoresist can be enlarged when the equivalent of acid and base which constitute the surfactant is made excess of base compared with acid upon a formation of a surfactant which is contained in the composition for preventing development defects, and the amount of film thickness reduction of a photoresist subsequent to a development can be increased or decreased by controlling the amount of the base used at this time, thus being achieved the present invention.